The present invention relates to an air control switch set for an overedge sewing (overlock) machine which is coupled between a motor and a pedal, and driven by the pedal to let air pass to the desired location prior to starting of the motor, enabling the thread head to be accurately cut.
A regular air control switch set for an overedge sewing machine, as shown in FIG. 1, comprises a base frame 90. The base frame 90 comprises staggered top wall 91 and bottom wall 92, and staggered upper partition wall 93 and lower partition wall 94 horizontally disposed at different elevations. A first air control valve 80 is mounted on the upper partition wall 93, which is spaced below the top wall 91. The first air control valve 80 comprises a switch 81 facing the top wall 91. A pull rod 95 is inserted through a hole at the top wall 91 and a hole at the upper partition wall 93, having a top end coupled to a motor (not shown) and a bottom end coupled to the bottom wall 92. Springs 96 are respectively mounted on the pull rod 95, and retained between the top wall 91 and the upper partition wall 93 and, the lower partition wall 94 and the bottom wall 92. A second air control valve 70 and a link 97 are mounted on the lower partition wall 94. The second air control valve 70 is connected to an air nozzle and thread suction device. The link 97 has one end fixedly connected to the lower partition wall 94, and an opposite end inserted through a hole on the bottom wall 92 and coupled to a pedal (not shown). The second air control valve 70 communicates with the an air compressor (not shown), and the first air control valve 80 at the upper partition wall 93. The second air control valve 70 comprises a switch 71 facing the bottom wall 92. When the pedal is pressed down, the link 97 is lowered, causing the pull rod 95 and the lower partition wall 94 to be lowered with the link 97. When the pull rod 95 is lowered with the link 97, the motor is started, and therefore the overedge sewing machine is driven to reciprocate the threaded needle, at the same time the switch 71 of the second control air valve 70 is pressed on the bottom wall 92 to open the second air control valve 70, enabling air to pass out of the second air control valve 70 to the air nozzle and thread suction device. This structure of air control switch set is still not satisfactory in function. During stitching operation, the operator must apply much effort to press down the pedal in lowering the link 97, enabling the switch 71 of the second control air valve 70 to be positively pressed on the bottom wall 92 to open the second air control valve 70. Because the top wall 91 and the pull rod 95 are simultaneously moved when the link 97 is pulled downwards by the pedal, the motor may be started before the second control air valve 70 is opened to let air pass to the air nozzle and thread suction device at the beginning of a stitching operation or during a slow stitching operation (for example, a curved or fancy stitching operation), causing the thread head unable to be properly cut.